White dwarf evolution in real time: What pulsating white dwarfs teach us about stellar evolution

Abstract

The photometric properties of the variable white dwarfs are reviewed along with pertinent theory. Consideration is given to behavior of the white dwarf variables, ranging from simple linear pulsators with pulsation spectra well described by linear theory to stars which undergo complex light variations that border on nonperiodic. In all of these pulsators, however, the observed pulsation characteristics show underlying regularity that can be attributed to linear normal mode pulsation, and these regularities make it possible to determine structural and evolutionary properties of white dwarf stars. The physical interpretation of white dwarf pulsation spectra is discussed, including mass and composition from period spacing, rotation rate and magnetic field strength from frequency splittings, evolutionary time scale from rates of period change, and thermal structure and composition from nonadiabatic considerations.